Medical retrieval devices generally are used to retrieve biological and foreign material from the body including stones. Such medical retrieval devices include, for example, retrieval baskets, and may be used through an endoscope or a laparoscope.
One type of known device has a sheath and a retrieval assembly such as a basket that is movable in and out of the sheath. When the basket is within the sheath, the basket assumes a collapsed, reduced diameter profile. When the sheath is retracted relative to the basket or the basket is moved beyond the end of the sheath, the basket expands to a relatively larger diameter than when the basket is enclosed within the sheath. Generally, the contour of known baskets is round or oval and is formed by a plurality of legs.
With many known retrieval devices, it is technically difficult to release captured material such as a stone from the retrieval assembly once the stone is captured. In some patients, a cicatrix, for example, or some other constriction that reduces the diameter of the lumen of the tract may form in the tract in which the stone is lodged because of recurrent trauma caused by the stone to the lining of the tract. The narrowed lumen of the tract may not be so narrow so as to interfere with insertion of a retrieval device while the retrieval device is in a collapsed position. However, after the retrieval device is inserted into the tract, the retrieval assembly expanded, and the stone captured within the device, the diameter of the retrieval assembly containing the stone may exceed the inner diameter of the narrowed lumen of the tract or the inner diameter of the orifice of the tract into which the retrieval device is inserted. If an excessive pulling force is used by the operator in an attempt to remove the retrieval device and stone, the retrieval device may traumatize the orifice or the lining of the tract or, worse, perforate the tract. In addition, the retrieval device may assume an everted configuration causing damage upon being withdrawn from the tract. Under these conditions, the stone must first be released from the retrieval device followed by withdrawal of the collapsed retrieval device from the tract. If the stone can not be released from the retrieval device, more invasive, surgical approaches are required to disengage the stone from the retrieval device and to remove the retrieval device from the body tract.
With most, if not all, current medical retrieval device designs, it is difficult to disengage the stone or other material from the retrieval assembly so that the retrieval device can be collapsed and then removed from the body. A medical retrieval device that is capable of collapsing to release a stone captured by the device in the body of a patient is needed. The device described herein addresses this need.